man3/malloc_info.3

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  25 .TH MALLOC_INFO 3  2019-03-06 "GNU" "Linux Programmer's Manual"
  26 .SH NAME
  27 malloc_info \- export malloc state to a stream
  28 .SH SYNOPSIS
  29 .nf
  30 .B #include <malloc.h>
  31 .PP
  32 .BI "int malloc_info(int " options ", FILE *" stream );
  33 .fi
  34 .SH DESCRIPTION
  35 The
  36 .BR malloc_info ()
  37 function exports an XML string that describes the current state
  38 of the memory-allocation
  39 implementation in the caller.
  40 The string is printed on the file stream
  41 .IR stream .
  42 The exported string includes information about all arenas (see
  43 .BR malloc (3)).
  44 .PP
  45 As currently implemented,
  46 .I options
  47 must be zero.
  48 .SH RETURN VALUE
  49 On success,
  50 .BR malloc_info ()
  51 returns 0;
  52 on error, it returns \-1, with
  53 .I errno
  54 set to indicate the cause.
  55 .SH ERRORS
  56 .TP
  57 .B EINVAL
  58 .I options
  59 was nonzero.
  60 .SH VERSIONS
  61 .BR malloc_info ()
  62 was added to glibc in version 2.10.
  63 .SH ATTRIBUTES
  64 For an explanation of the terms used in this section, see
  65 .BR attributes (7).
  66 .TS
  67 allbox;
  68 lb lb lb
  69 l l l.
  70 Interface       Attribute       Value
  71 T{
  72 .BR malloc_info ()
  73 T}      Thread safety   MT-Safe
  74 .TE
  75 .sp 1
  76 .SH CONFORMING TO
  77 This function is a GNU extension.
  78 .SH NOTES
  79 The memory-allocation information is provided as an XML string
  80 (rather than a C structure)
  81 because the information may change over time
  82 (according to changes in the underlying implementation).
  83 The output XML string includes a version field.
  84 .PP
  85 The
  86 .BR open_memstream (3)
  87 function can be used to send the output of
  88 .BR malloc_info ()
  89 directly into a buffer in memory, rather than to a file.
  90 .PP
  91 The
  92 .BR malloc_info ()
  93 function is designed to address deficiencies in
  94 .BR malloc_stats (3)
  95 and
  96 .BR mallinfo (3).
  97 .SH EXAMPLE
  98 The program below takes up to four command-line arguments,
  99 of which the first three are mandatory.
 100 The first argument specifies the number of threads that
 101 the program should create.
 102 All of the threads, including the main thread,
 103 allocate the number of blocks of memory specified by the second argument.
 104 The third argument controls the size of the blocks to be allocated.
 105 The main thread creates blocks of this size,
 106 the second thread created by the program allocates blocks of twice this size,
 107 the third thread allocates blocks of three times this size, and so on.
 108 .PP
 109 The program calls
 110 .BR malloc_info ()
 111 twice to display the memory-allocation state.
 112 The first call takes place before any threads
 113 are created or memory allocated.
 114 The second call is performed after all threads have allocated memory.
 115 .PP
 116 In the following example,
 117 the command-line arguments specify the creation of one additional thread,
 118 and both the main thread and the additional thread
 119 allocate 10000 blocks of memory.
 120 After the blocks of memory have been allocated,
 121 .BR malloc_info ()
 122 shows the state of two allocation arenas.
 123 .PP
 124 .in +4
 125 .EX
 126 .RB "$ " "getconf GNU_LIBC_VERSION"
 127 glibc 2.13
 128 .RB "$ " "./a.out 1 10000 100"
 129 ============ Before allocating blocks ============
 130 <malloc version="1">
 131 <heap nr="0">
 132 <sizes>
 133 </sizes>
 134 <total type="fast" count="0" size="0"/>
 135 <total type="rest" count="0" size="0"/>
 136 <system type="current" size="135168"/>
 137 <system type="max" size="135168"/>
 138 <aspace type="total" size="135168"/>
 139 <aspace type="mprotect" size="135168"/>
 140 </heap>
 141 <total type="fast" count="0" size="0"/>
 142 <total type="rest" count="0" size="0"/>
 143 <system type="current" size="135168"/>
 144 <system type="max" size="135168"/>
 145 <aspace type="total" size="135168"/>
 146 <aspace type="mprotect" size="135168"/>
 147 </malloc>
 148
 149 ============ After allocating blocks ============
 150 <malloc version="1">
 151 <heap nr="0">
 152 <sizes>
 153 </sizes>
 154 <total type="fast" count="0" size="0"/>
 155 <total type="rest" count="0" size="0"/>
 156 <system type="current" size="1081344"/>
 157 <system type="max" size="1081344"/>
 158 <aspace type="total" size="1081344"/>
 159 <aspace type="mprotect" size="1081344"/>
 160 </heap>
 161 <heap nr="1">
 162 <sizes>
 163 </sizes>
 164 <total type="fast" count="0" size="0"/>
 165 <total type="rest" count="0" size="0"/>
 166 <system type="current" size="1032192"/>
 167 <system type="max" size="1032192"/>
 168 <aspace type="total" size="1032192"/>
 169 <aspace type="mprotect" size="1032192"/>
 170 </heap>
 171 <total type="fast" count="0" size="0"/>
 172 <total type="rest" count="0" size="0"/>
 173 <system type="current" size="2113536"/>
 174 <system type="max" size="2113536"/>
 175 <aspace type="total" size="2113536"/>
 176 <aspace type="mprotect" size="2113536"/>
 177 </malloc>
 178 .EE
 179 .in
 180 .SS Program source
 181 .EX
 182 #include <unistd.h>
 183 #include <stdlib.h>
 184 #include <pthread.h>
 185 #include <malloc.h>
 186 #include <errno.h>
 187
 188 static size_t blockSize;
 189 static int numThreads, numBlocks;
 190
 191 #define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \e
 192                         } while (0)
 193
 194 static void *
 195 thread_func(void *arg)
 196 {
 197     int j;
 198     int tn = (int) arg;
 199
 200     /* The multiplier \(aq(2 + tn)\(aq ensures that each thread (including
 201        the main thread) allocates a different amount of memory */
 202
 203     for (j = 0; j < numBlocks; j++)
 204         if (malloc(blockSize * (2 + tn)) == NULL)
 205             errExit("malloc\-thread");
 206
 207     sleep(100);         /* Sleep until main thread terminates */
 208     return NULL;
 209 }
 210
 211 int
 212 main(int argc, char *argv[])
 213 {
 214     int j, tn, sleepTime;
 215     pthread_t *thr;
 216
 217     if (argc < 4) {
 218         fprintf(stderr,
 219                 "%s num\-threads num\-blocks block\-size [sleep\-time]\en",
 220                 argv[0]);
 221         exit(EXIT_FAILURE);
 222     }
 223
 224     numThreads = atoi(argv[1]);
 225     numBlocks = atoi(argv[2]);
 226     blockSize = atoi(argv[3]);
 227     sleepTime = (argc > 4) ? atoi(argv[4]) : 0;
 228
 229     thr = calloc(numThreads, sizeof(pthread_t));
 230     if (thr == NULL)
 231         errExit("calloc");
 232
 233     printf("============ Before allocating blocks ============\en");
 234     malloc_info(0, stdout);
 235
 236     /* Create threads that allocate different amounts of memory */
 237
 238     for (tn = 0; tn < numThreads; tn++) {
 239         errno = pthread_create(&thr[tn], NULL, thread_func,
 240                                (void *) tn);
 241         if (errno != 0)
 242             errExit("pthread_create");
 243
 244         /* If we add a sleep interval after the start\-up of each
 245            thread, the threads likely won\(aqt contend for malloc
 246            mutexes, and therefore additional arenas won\(aqt be
 247            allocated (see malloc(3)). */
 248
 249         if (sleepTime > 0)
 250             sleep(sleepTime);
 251     }
 252
 253     /* The main thread also allocates some memory */
 254
 255     for (j = 0; j < numBlocks; j++)
 256         if (malloc(blockSize) == NULL)
 257             errExit("malloc");
 258
 259     sleep(2);           /* Give all threads a chance to
 260                            complete allocations */
 261
 262     printf("\en============ After allocating blocks ============\en");
 263     malloc_info(0, stdout);
 264
 265     exit(EXIT_SUCCESS);
 266 }
 267 .EE
 268 .SH SEE ALSO
 269 .BR mallinfo (3),
 270 .BR malloc (3),
 271 .BR malloc_stats (3),
 272 .BR mallopt (3),
 273 .BR open_memstream (3)